Laboratoire de Physique Théorique
Toulouse - UMR 5152

A magnetic impurity on a conventional superconductor is one of the most simple pair-breaking defects that induces in-gap Yu-Shiba-Rusinov (YSR) bound states, whose intricate spatial structure crucially influences the possibilities of engineering collective impurity states (e.g., Shiba chains, lattices...) and topological superconductivity.

In this talk, I will first introduce the paradigmatic model used to describe a magnetic impurity on a two-dimensional superconductor and I will discuss the main aspects of the YSR physics. Secondly, I will present our recent work on the quasiparticle effect of YSR states, where we use a generalized saddle-point approximation to unveil a simple analytical relationship between the spatial structure of the YSR bound states and the momentum-space anisotropy of the Fermi surface, namely the angular dependent Fermi velocity and curvature of the Fermi surface.

I will show that our analytical approximation is quantitatively accurate against tight-binding calculations in lattice models and I will discuss its application to describe the anisotropy of YSR states observed in scanning tunneling spectroscopy experiments of magnetic impurities on NbSe2.